While conventional engineering materials typically have an elastic limit much less than 1% strain, nitinol can experience fully recoverable strains up to 8%. This capability allows a properly designed nitinol component to radically transform its shape during service, fueling the trend toward minimally invasive procedures. For example, a nitinol stent may be designed to be delivered through a 2-mm sheath and expand to support a 10-mm vessel. Similarly, an endoscopic instrument may be delivered through a 15-mm instrument, expand to 60 mm to retrieve a specimen, and then collapse to exit through a similarly sized port.

In short, if a medical component must be delivered in a compressed state and then become an expanded shape, nitinol is likely to offer design advantages unavailable with other materials.

Finding the right balance of dye is critical. One way to judge the impact of the dye in the plastic or the transmission through the plastic is to measure the intensity of light coming through the plastic from the light source. You can calculate a percentage loss of transmission through the plastic in both the UV and visible regions. Most adhesives want to see a minimum of 200 mW/cm², and some of the light sources on the market emit light of 20,000 mW/cm². Even if the plastic blocks off 90% of the UV light and 70% of the visible light, this might be enough to allow the adhesive to cure.

If the plastic compounder uses a pigment to augment the tint, make sure that the level of the pigment is low and that it contains a material such as titanium dioxide.

A good field test is to hold the plastic up to the light. If you can see a shadow as you wave your hand behind it, you might have enough light coming through to cure the adhesives. Stay away from yellow-orange-red colors. Whites, blues, and greens are better. A number of medical grade adhesives and various curing lamps can be used for this application. I might recommend contacting Dymax Application Engineering to arrange for some free samples and to discuss the Try/Rent lamp program.

Thus, the question becomes: How long should the adhesive survive at 1400°F? If the answer is minutes, finding a material that can survive short bursts of high temperatures for only a little while may be sufficient. For this purpose, a number of different chemistries, such as silicone or epoxy, are available. Typically, unfilled organic adhesives such as acrylics and urethanes will break down long before they reach 1400°F.

The last question is: What are the properties needed? Does the adhesive need to be clear, or is opaque acceptable? How do you want to remove the material? Unfortunately, there is no simple answer to these questions. The technical support groups at the companies mentioned above may be able to help further or recommend options for you to consider.

There can be what might seem as an overwhelming number of factors associated with the life of a motor and/or gearbox in any specific medical application. Life is entirely application dependent; the life of a motor can vary from quite short to very long—potentially tens of thousands or even hundreds of thousands of hours. Factors such as current draw and electrical load, speed, type of operation (continuous- or intermittent-duty cycle), temperature, humidity, vibration, type of installation, brush type, lubricants used, thermal management and heat sinking, and axial and radial loading are typical factors that will come into play. Brushless motors have the longest potential life, since the life of a brushless motor is generally limited to the life of the ball bearings. If properly sized, a brushless motor can reliably run for many years continuously. In contrast, a brushed motor generally has a life span limited to the life of the brushes. If a gearbox is used in combination with either a brush or brushless motor, it may become the life-limiting factor.

It is nearly impossible to theoretically determine motor life in any specific application; every application and the related performance required are unique. However, many things can be done to maximize motor life and reliability, which is critically important for medical products. First, consider only the highest-quality motion control products that have a strong presence in the medical market and ISO 13485 quality certification. Design the device using brushless rather than brushed motors, and be sure that the motor and gearbox are rated conservatively for the application’s loading and performance. Gearbox input speeds and axial/radial loading should be minimized, and all potential environmental factors should be considered. Theoretical ball bearing calculations can be performed, but they often do not produce realistic figures, since they do not take such factors as lubricant deterioration, lubricant contamination, or the type of lubricant into account.

Ultimately motor life can only be determined confidently through actual and extensive life testing—most importantly, by simulating application circumstances and environments that are identical to real conditions. In combination with the motor manufacturer’s engineering support and destructive analysis of motor and gearbox parts following life tests, the actual wear of potential life-limiting parts such as bearings and brushes can be measured. By comparing this information with the relative number of test hours, motor life can be estimated most accurately.

Solvent grades are typically not listed as medical grade or FDA approved but rather by the purity level of the solvent. Obtaining the solvent of choice with the highest purity (99.9% or higher) would limit the potential of leaching chemicals into the water. Sigma Aldrich or Alpha Aesar both provide small quantities of these solvents in various grades for evaluation purposes. Methyl ethyl ketone is an alternative solvent system. However, because of their odor, flammability, and explosive-material storage requirements, using solvents requires special handling and is carefully monitored by the EPA. Dispensing systems such as those offered by Tecnoideal are options to limit operator exposure.

If you want to consider a solvent-free adhesive, looking at a one-part light-curable adhesive such as Dymax’s 1161-M is possible if you can get visible light to the bond line (the nonopaque parts). Alternatively, a two-part urethane or epoxy from companies such as Epoxy Technology or 3M (to name two options) can be considered. These alternatives can provide a bond almost as strong as that provided by a solvent and with fill gaps in the molded ABS bond lines. In addition, they are much more environmentally friendly.